Certain other two-phase electrolysis systems are already known. For instance, the mercury cell commonly used for the electrolysis of sodium chloride solutions to produce chlorine and sodium amalgam, and eventually sodium hydroxide, utilizes two phases, i.e., the aqueous sodium chloride and the metallic mercury. In this case, however, the mercury phase conducts electronically, i.e., by the movement of electrons as in any conducting metal. In reality the mercury phase behaves as a liquid cathode. Also in the sodium hydroxide - chlorine industry, electrolyses using two aqueous phases separated by an ion exchange membrane have been used. Here the sodium chloride solution forms the anolyte, evolving chlorine at the anode therein; the electrolyte on the other side of the membrane is aqueous sodium hydroxide in which there is a cathode evolving hydrogen. Thus, these are both aqueous phases, and but for the ion exchange membrane, the same would be miscible with each other.
Such systems are severely limited in regard to the types of electrochemical processes which can be conducted therein.
A further common and well known problem, typically in organic electrochemistry is in dealing with the oxidation or reduction of water insoluble species. Due to the typically dielectric character of, for instance, organic liquids, electrolysis techniques are generally unsatisfactory. Usually the approach to overcome, to some extent, this difficulty is to use a water-miscible co-solvent, e.g., ethanol or acetone, to co-solve the water-insoluble species in the aqueous phase. Another technique is to use a solubilizing compound such as an aromatic sulphonic acid which co-solves the insoluble species and which can also act as the electrolyte. Both these techniques are intended to produce a single water-miscible phase for the electrolysis, and the same are also limited in their applications. See, for example, Organic Electrochemistry, by M.M. Baizer Ed., published by Dekker, New York, 1973.